Liquid phase relationships in fertilizer granulation by a layering process

Abstract

In certain variants of the fertilizer granulation process granulation occurs by deposition of a layer of raw material onto a previously formed nucleus. An expression for the liquid phase required for layering as a function of the proportion of nuclei present has been derived from a simple model of the layered granule and tested against laboratory simulation experiments on glass beads and sand. The expression is applied to fertilizer granulation to define the range of conditions over which layering is possible and the recycle ratios required as a function of fertilizer solubility and the water entering the granulator. Layering requires a higher recycle ratio than the corresponding agglomeration process, but in general gives product with better storage properties and shorter drying time. The economics of the process depend on the saving in drying costs compared to the cost of extra conveying equipment. Modifications to the basic process to improve its economics are considered briefly.